Increasing applications of electric motors and the environmental problems associated with the production of electric energy in Power plants, together with the rapid increase in energy cost necessitate the development of new methods for designing and constructing of energy efficient motor drives. Optimal control of motors efficiency by minimization of electrical losses is an effective means for realizing this purpose. In this paper, after presenting a dynamic model of 3-phase induction motors including copper and iron losses, the motor electrical loss is analyzed as a function of motor variables, and the conditions of its minimization are described. A new control system for finding the minimum loss point and as a result the on-line optimization of motor efficiency at variable speed and load is then proposed. In this system, a motor control variable changes continuously in search for the minimum loss point. This new method, in comparison with existing on-line loss minimization methods of induction motors, leads to a more energy saving and a smoother motor operation. The comparison of simulation results of a vector controlled induction motor under the proposed control system and a conventional control system confirms the superiority of the proposed system.
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